The specialized plaque regions of the urothelial plasma membrane contain linear arrays of hexagonal particles. Each plaque particle appears as a hexagon comprising twelve subunits. We believe that the 24,000 dalton protein species dominating the sodium dodecyl sulfate polyacrylamide gel electrophoretic pattern of the plaque regions is a likely candidate for basic subunit making up the plaque particle. Thus, we are immediately concerned with the isolation of the 24,000 dalton protein in pure form. We will then attempt to show this 24,000 dalton protein is the basic dodecameric subunit making up the plaque particle. Using the 24,000 dalton protein as antigen, we will prepare antibodies specific to this subunit structure. We then plan to conjugate the antibody with fluorescent markers which can be visualized microscopically. Next, we will attempt to localize immunocytochemically the protein subunit (a) in the isolated plasma membrane, (b) in the lumenal surface membrane of the intact bladder and (c) within the urothelial cells, thus possibly demonstrating the steps involved in the synthesis of the protein subunit and its incorporation into membrane structure. BIBLIOGRAPHIC REFERENCES: Caruthers, J.S. and M.A. Bonneville, 1977. Isolation and characterization of the Urothelial lumenal plasma membrane. J. Cell Biol., 73: 382-399. Caruthers, J.S. and M.A. Bonneville, 1976, Characterization of plaque regions of sheep bladder lumenal plasma membrane. J. Cell Biol., 70: 298a (abstract).